<p>Don't get me wrong, I loved the book, even the last third, which I think was set up nicely by the first two thirds. I have no problem with the psychological differentiation of the races. They had a thousand years of messing with their genomes during the age of isolation. (As per textev) And at least half of it would be cultural anyway.</p><p>1. The biggest problem I think was that Izzy wold be just as fried by the white sky as the Earth's surface. The sky takes up a fraction more than 180 degrees from the point of view of someone on the surface. From the point of view of Izzy at 400 km altitude, the atmosphere takes up a fraction less than 180 degree. Not much difference. They'd be fried just as crisply. The radiant energy of the white sky goes in all directions.<br></p>

The day before The Break, the day the White Rain started, Ivy and Dinah both report on how they need to begin moving away from Earth as the atmosphere is showing evidence of expanding. This was something they expected and were prepared for. There is a reference to needing enough coolant to get the entire ark "higher".

<p>6. Boiling the oceans. Where did the water go? It boiled off into the atmosphere, but when the surface cooled down, it would rain out back and refill the oceans. Unless some of the H2O was fractured in the high atmosphere (by ultraviolet?) and the hydrogen lost. This is IIRC how Mars lost it's water. But then what happened to the excess oxygen? If it was only a little (gigatons) then the comets were only to top off the oceans. dunno.<br></p>

<p>5. The underground shelter in the book gets their power from geothermal. You can only generate power from temperature differentials. You need someplace hot and someplace cold, relatively anyway. The surface would be roasting and after a while the heat would penetrate some way down. I don't know how much. Any shelter would be between a rock and a hard place. You have heat coming up from below, deep mines always get hot the deeper you get. So you would have to find some kind of temperature differential to run your generators and then run a massive refrigeration plant off of that, and find some place to dump the heat. Maybe that's why the governments preferred to invest in shelters at the bottom of ocean trenches.That might work better.<br></p>

<p>3. And what about Orion? It would have been ideal for the situation. I was looking forward to lifting a few million tons into orbit by blasting a-bombs underneath thick concrete, steel and lead plates. See Footfall by Niven and Pournelle. It would explain nicely why the powers that be didn't seem too concerned by the logistics of long-term survival in orbit. A half million tons of ice would go a long way. And they would leave Orion till the last minute to avoid freaking everybody out. (and it would kill a lot of people) Oh, well.<br></p>

<p>4. Why would there only be one underground safe haven built? That survived anyway. Another reason that governments would see Izzy and the arklets as a distraction for the populace would be that they were pouring most of their efforts into habitats in deep existing mines and the like. Much easier to move millions of tons of needed stuff and thousands of people underground than into orbit. Seems obvious.<br></p>

<p>2. The first thing I thought of when the moon broke up was that you now have a chaotic multi-body gravitational problem. These things are not predictable even theoretically. You could have a chunk slingshotted off in some random direction by the orbital interactions of the seven, then dozens of pieces of the moon. Even a 50th chunk of moon slamming into the earth would leave nothing left but a very short book.<br></p>